When should i switch to a flowering light cycle?

Yes. If you cannot raise the light any further than what is pictured in your diary, you're going to have a very rough time. Cannabis (especially sativa dominant genetics) will grow two to three times its size in only 4-5 weeks after the flip to 12/12. You're looking at your top buds literally growing into your light. You'll definitely need to do some heavy training. I suggest that you continue to tie down the branches, even more so than you've done already. I would also suggest you bend the main stem down as far as it can go without snapping and tie it down as well. You could also top the plant again at the main stem a few inches below the top to help control the height. Your plant looks healthy, although small and stretchy for a 10 week veg time. I'm no expert and don't know the exact specifics of your grow, but If I had to take a guess its probably due to your light. Weak lighting will make your plants grow tall without much foliage. The plant senses that its not getting enough light, so it naturally tries to grow tall to get the light it needs. This makes the stems weak and the plant lanky. I would recommend at minimum a 100W LED for a 2x2 growing space, with 150W+ being ideal. Your plant will produce buds, however I wouldn't expect anything crazy. For a first grow you're doing pretty good though and you've got the right ideas. I hope this helps and happy growing friend. 😁